Chemicals have long been administered to treat or prevent illness. Chemotherapy is optimized by carefully controlling the amount, timing and location in the body of drug dosing. Implanted vascular access devices (VADs) are particularly useful for the prolonged, repeated or targeted injection of medications, sparing a patient the constant search for peripheral veins to achieve venous access. Moreover, VADs obviate the need for a dressing to cover the access site, once the incision from implantation of the device heals.
VADs typically include a catheter and an access or infusion port. The catheter of the VAD is implanted in fluid communication with an artery or vein, while the infusion port is implanted below the skin of the patient. Access to the port, and thereby to the catheter and the artery or vein, is obtained by puncturing the skin with a needle or cannula, until fluid communication with the port is achieved. Typically, the infusion port has an internal infusion chamber in fluid communication with the catheter, sealed or covered by a self-healing top septum, and the needle or cannula pierces the septum to achieve the ultimately desired access to the patient's vascular system.
While conventionally referred to as "infusion" ports, the ports of VADs are also useful for blood sampling and for the supply of blood products and nutrients. Reference to "infusion" ports throughout this application therefore includes ports useful or used for these other purposes, in addition to infusion.
It is important that the infusion port of the VAD is implanted deeply enough to avoid necrosis of the overlying tissue and erosion of the port through the skin, typically, at least about 12 to 13 mm beneath the skin of the patient. While this usually avoids tissue necrosis, it also makes it difficult to visually determine the site of the desired injection site, that is, the site of the infusion port and septum. This is particularly difficult since the sutured incision or scar from the implantation of the VAD is not an adequate guide to the precise location of the port or septum. (Whether the implantation site will have a sutured incision or a scar depends upon the length of time that has passed since implantation of the VAD.) Indeed, it is highly preferred during implantation of a VAD that the port is offset from the incision, precisely to avoid injections through the sutured incision or scar.
Because of the depth of implantation of the port, the conventional method of piercing the skin over the port and septum entails repeated manual palpation of the site. The site is first palpated to generally locate the port, and then palpated a second time (after site sterilization) to precisely locate the port and septum and stabilize their position during introduction of the needle or cannula. This conventional method is subject to some drawbacks, however. It involves repeated contact with the patient's skin, prolonged positioning of the fingers near the site, and prolonged positioning of the fingers nearer the needle or cannula than might be desired. All of these increase the possibility of contamination of the site or cross-contamination of the person performing the injection. Of course, palpation is made even more difficult when a low-profile infusion port is used, but low-profile ports are highly desirable because they require a relatively smaller subcutaneous pocket during implantation.
Numerous devices exist to aid piercing the skin with a needle or cannula and engaging an implanted VAD. One such device is shown in U.S. Pat. No. 4,813,939 (Marcus, Mar. 21, 1989). That patent is directed to an infusion apparatus for use with implantable access ports. The infusion apparatus includes a disc housing and wings hingedly secured to the housing for convenient grasping of the apparatus during use. While useful for its intended purpose, this device and devices like it do not have any provision for visually locating a subcutaneously implanted infusion port, nor for stabilizing the port itself against underlying tissue or against the pressure needed to introduce the needle or cannula.